The Acetonitrile Problem

With no end in sight to the worldwide shortage of acetonitrile, the popular high performance liquid chromatography (HPLC) solvent, laboratories are in search of cost-effective solutions to manage the impact on their research and business timelines.  The emerging innovations represent yet another example of how more cost effective and “greener” laboratory practices are advancing the field of analytical chemistry, especially in HPLC analysis.

The pharmaceutical industry consumes approximately 70 percent of the world’s supply of acetonitrile, using the solvent in a range of applications in both manufacturing and analytical settings. Acetonitrile is commonly used in Gas Chromatography (GC) analysis, Ultraviolet (UV) analysis, Thin Layer Chromatography (TLC) and High Performance Liquid Chromatography (HPLC) applications as well as other wet chemistry test methods in the laboratory.  Acetonitrile is currently the chosen solvent of today’s HPLC analyses, largely due to its miscibility with both water and most organic solvents and to its low toxicity, viscosity and chemical reactivity.  Acetonitrile is also used in the synthesis and manufacturing of drug substances and drug products.

Global Events

The “Great Acetonitrile Shortage,” as it has come to be known by suppliers, arose due to a series of events in 2008.  Chinese production of Acetonitrile dropped significantly in preparation for hosting the 2008 Summer Olympics in Beijing. Chinese factories in the vicinity, including China’s largest Acetonitrile producer, were shut down to minimize air pollution.  After the Olympics, Acetonitrile export from China was significantly limited by newly implemented import bans.  At the same time, Acetonitrile manufacturing in Texas was interrupted due to active hurricanes in the Gulf of Mexico.  Yet possibly the most substantial and long-lasting impact on the Acetonitrile supply was triggered by the worldwide economic slowdown that started in 2008. 

Acetonitrile is a by-product of the synthesis of acrylonitrile. In this process, acrylic fibers and acrylonitrile-butadiene-styrene resins are used to manufacture plastics for automobiles, carpeting, luggage, telephones, computer housings, and other products.   Due to the economy, consumer purchasing and manufacturing production of these items has slowed. Lessening demand has prompted the world’s acrylonitrile producers to also slow production. As a result, fewer resources are being invested in collecting and purifying Acetonitrile to the high purity grades required by the pharmaceutical industry. 

Impact in the Lab

As a consequence of these events, the prices for high-quality and HPLC-grade Acetonitrile have sky-rocketed throughout 2009, with prices of Acetonitrile increasing from $30/liter to $100/liter between July and September.  As the major Acetonitrile producers ration their supplies, they have started advising customers to develop alternative methods to eliminate or reduce the use of Acetonitrile.  Although the long-term forecast of cost and availability is still uncertain, the general feeling is that Acetonitrile prices will continue to rise and many labs will find it difficult to acquire the quantities needed to perform their manufacturing and testing as cost-efficiently as is the past.

The pharmaceutical industry relies on Acetonitrile for a wide range of applications including many that must be conducted under Current Good Manufacturing Practices (CGMP).  Consequently, the scarceness of this single industrial chemical has the potential to delay progress.  From a drug development standpoint, it can impact the timelines for application approvals and delay market launches.  For current, agency-approved products, it will become the norm for companies to manufacture fewer batches to reduce the amount of testing.

The United States FDA has received numerous inquiries related to the Acetonitrile shortage, primarily around the solutions that companies are allowed to apply to their already-validated methods that require Acetonitrile.  The FDA response has been cautious, “regardless of the changes a firm makes to address the shortage, appropriate method validation and compliance with relevant good manufacturing practices (CGMPs) are necessary.”  Changes made to existing validated test methods within an approved application (New Drug Application (NDA) or Abbreviated New Drug Application (ANDA)) to accommodate using less Acetonitrile or an alternative solvent to Acetonitrile may be as simple as a minor change in the Annual Report for the given drug application as long as the change meets the criteria stated in the US FDA Guidance for Industry, “Changes to an Approved NDA or ANDA,” and Code of Federal Register title 21CFR314.70(d)(2)(vii).  The guidance and CFR allow “A change in an analytical procedure used for testing….that provides the same or increased assurance of identity, strength, quality, purity, or potency of the material being tested…If the same or increased is not achieved, prior approval supplement will be required.”¹

As the shortage of Acetonitrile continues with no relief in sight, the pharmaceutical industry is motivated to locate both short- and long-term solutions to minimize reliance on Acetonitrile.

Recommended Solutions

Outsourcing

Companies using Acetonitrile with CGMP-validated HPLC methods that are already submitted in application have two options. These companies can either continue to pay the current high (and escalating) prices to secure a continued supply of Acetonitrile or they can modify their methods to remove or reduce their use of Acetonitrile based on a risk-benefit analysis.  In the latter instance, companies without extensive understanding of the regulatory guidelines and HPLC technology may strategically opt to partner with an analytically-focused contract laboratory facility that is versed in up-to-the-minute regulatory guidelines and HPLC method optimizations to help reduce their use of Acetonitrile. By outsourcing to a contract laboratory, CGMP HPLC projects can minimize the delays that many small and large pharmaceutical companies are experiencing as a result of the shortage.

For companies committed to finding a long-term, cost-effective solution that minimizes their use of Acetonitrile as an HPLC solvent, the contract laboratory can explore either replacing Acetonitrile with a more widely-available solvent or identifying a method optimization to significantly reduce overall solvent consumption.  

Solvent Replacement

For solvent replacement, three fundamental factors need to be considered:  (1) the chemical properties of the solvent, (2) the physical properties of the solvent, and (3) the effects these properties have on the chromatographic process (e.g. separation, detection limits, and analytical reproducibility).   Unfortunately, Acetonitrile has no equivalent substitute in the reverse-phase (RP) HPLC ultraviolet (UV) application where it is most heavily employed.  The superior UV absorbance characteristics and solubilizing properties of Acetonitrile are unmatched among other solvents.  However, depending upon the chromatography type and the detection wavelengths in use, it may be possible to replace Acetonitrile with methanol or with a longer chain alcohol.  However, because of methanol’s significant absorbance up to 215 nm, its use as a substitute for Acetonitrile is restricted to situations either working at > 235 nm or limiting the methanol level in the mobile phase to less than 15% at = 215 nm.  Tetrahydrofuran (THF) is also a viable substitute, although drawbacks associated with unpreserved or UV-grade THF make it significantly less preferred than methanol. 

Solvent Reduction

As solvent replacement can significantly impact method performance and specificity/robustness, it is not technically feasible in many situations. It is often less complicated to optimize a method for reduced solvent consumption.  Reduced consumption patterns are further supported by many pharmaceutical companies’ commitments to “greener” strategies in an effort to minimize pollution and waste.  There are three approaches to reducing the use of Acetonitrile: (1) simple changes to what occurs pre- and post-separation ; (2) method changes that reduce the overall amount of the mobile phase that is needed; and (3) a reduction of the percent of Acetonitrile that is required for effective separation. 

First, an analysis of what occurs pre- and post-separation can lead to significant reductions in Acetonitrile use.  For Reversed Phase (RP) column equilibration, for example, most modern columns can be equilibrated using only 10 column volumes. Methods should also be evaluated to minimize run times after final peak elution, possibly utilizing more needle wash capabilities prior to the next injection. Finally, for optimal solvent conservation, solvent recycling technologies that collect Acetonitrile can be used as long as the components of the mobile phase remain separate from each other.

Method changes that can reduce Acetonitrile usage can be grouped into those that generally may and those that may not affect specificity/robustness.  One of the most common changes that significantly reduces the amount of mobile phase without significantly affecting specificity/robustness is to reduce the column’s internal diameter (I.D.). For example, a 2.1 mm I.D. column consumes nearly five-fold less mobile phase than the more commonly used 4.6 mm column. Thus, this altered analytical method represents an 80% reduction in Acetonitrile usage.  This approach, however, will require instrument parameter adjustments in the method (i.e. flow rate) as well as to the analytical system (i.e. smaller diameter tubing, connectors and microflow detector cells) in order to achieve similar separation and pressure criteria required by the method. The dwell volume should also be scaled down by using smaller volume mixing chambers when gradient programs are required

Alternate HPLC Applications

Although lowering the column I.D is the easiest approach, it does present limitations.  An alternative is Ultra Fast HPLC (UHPLC).  Ultra Fast HPLC involves smaller particle sizes and smaller columns.  The UHPLC approach minimizes solvent usage while optimizing peak separation ability.  By combining UHPLC with new column technologies, HPLC separations can now be far more efficient. Separations that were not possible in the past are now achievable – and with less solvent use. 

In addition to the Ultra Fast HPLC, technological advances on HPLC packing materials, such as Fuse Core particle technologies, have been specially developed for hyper fast chromatographic separations and universal detection.  While UV detection is the most widely used of the HPLC applications, it has significant limitations because the absorbance of UV light is dictated by molecular structure.  By using “universal” detector technologies such as evaporative light scattering detectors (ELSD) and chemiluminescent nitrogen detectors (CLND), scientists can measure the electrical charge that is associated with analyte particles.  The charge is in direct proportion to the amount of the analyte in the sample and remains consistent, regardless of the compound.  The result is that universal detection can “see” any non-volatile analyte, including those without chromophores, thus reducing dependence on highly polarized solvents like Acetonitrile and offering a wider range of usable solvents.

Conclusion

The pharmaceutical industry is under pressure to find cost-effective solutions around the current Acetonitrile shortage.  As illustrated, adjusting to this new reality may require innovative changes in analytical methodology.  The ability of pharmaceutical companies to select the best strategy to meet their unique product goals and testing timelines can be greatly enhanced by aligning with a reputable and knowledgeable contract laboratory.  With appropriate guidance, a successful Acetonitrile reduction or replacement program can become a competitive advantage. Moreover, reducing the use of Acetonitrile is consistent with a broader move towards “green” industry practices by significantly reducing waste and inefficiency. In short, the global challenge of Acetonitrile is an opportunity for optimization and innovation.

 [1] Food & Drug Administration. “Acetonitrile Shortages: Recommendations for Reporting Changes in Analytical Procedures.”  Available at www.fda.gov/downloads/AboutFDA/CentersOffices/CDER/UCM171776.pdf. (Accessed on September 14, 2009.)

About the Author

Rosa Bonilla is director of Chemical Sciences for the Celsis Analytical Services facility in Edison, New Jersey.  Experienced in analytical method development, method validation, raw material characterization, impurity identification and instrumentation, Ms. Bonilla has a strong background in research and development and working in facilities under current good manufacturing practice (CGMP) environments. Contact at Celsis at 1-732-346-5100 or LABinfo@celsis.com.

About Celsis Analytical Services

Celsis Analytical Services is an accredited, CGMP contract laboratory with facilities in Edison, New Jersey and St. Louis, Missouri. A division of Celsis International, the company’s other divisions include:  Celsis In Vitro Technologies, supplying market-leading ADME-Tox products and services to speed drug development and discovery; and Celsis Rapid Detection, the leading global provider of rapid microbial systems for detecting contamination in consumer-bound products. For more information visit the company website at www.celsis.com.